[RFC PATCH 31/53] netfs: Provide netfs_file_read_iter()

[David Howells]

Provide a top-level-ish function that can be pointed to directly by
->read_iter file op.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Jeff Layton <jlayton@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
cc: linux-mm@xxxxxxxxx
---
 fs/netfs/buffered_read.c | 33 +++++++++++++++++++++++++++++++++
 include/linux/netfs.h    |  1 +
 2 files changed, 34 insertions(+)

diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
index 374707df6575..ab9f8e123245 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -564,3 +564,36 @@ int netfs_prefetch_for_write(struct file *file, struct folio *folio,
 	_leave(" = %d", ret);
 	return ret;
 }
+
+/**
+ * netfs_file_read_iter - Generic filesystem read routine
+ * @iocb: kernel I/O control block
+ * @iter: destination for the data read
+ *
+ * This is the ->read_iter() routine for all filesystems that can use the page
+ * cache directly.
+ *
+ * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall be
+ * returned when no data can be read without waiting for I/O requests to
+ * complete; it doesn't prevent readahead.
+ *
+ * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O requests
+ * shall be made for the read or for readahead.  When no data can be read,
+ * -EAGAIN shall be returned.  When readahead would be triggered, a partial,
+ * possibly empty read shall be returned.
+ *
+ * Return:
+ * * number of bytes copied, even for partial reads
+ * * negative error code (or 0 if IOCB_NOIO) if nothing was read
+ */
+ssize_t netfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct netfs_inode *ictx = netfs_inode(iocb->ki_filp->f_mapping->host);
+
+	if ((iocb->ki_flags & IOCB_DIRECT) ||
+	    test_bit(NETFS_ICTX_UNBUFFERED, &ictx->flags))
+		return netfs_unbuffered_read_iter(iocb, iter);
+
+	return filemap_read(iocb, iter, 0);
+}
+EXPORT_SYMBOL(netfs_file_read_iter);
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index e2a5a441b7fc..6e02a68a51f7 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -384,6 +384,7 @@ struct netfs_cache_ops {
 
 /* High-level read API. */
 ssize_t netfs_unbuffered_read_iter(struct kiocb *iocb, struct iov_iter *iter);
+ssize_t netfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter);
 
 /* High-level write API */
 ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,